Quote from Amuris
I hope not. They don't have anything to hint at any other villains. You can tell that Kudo isn't sure what is going to happen next. If it doesn't end after Aizen the story would be screwed up and wouldn't be interesting anymore if it still is. It's been written into a corner. Nothing can extend it other than dragging out the fight.
I don't think end with aizen because there's other think that still unknown such as the king and his guard. Maybe the king is the real villian here..
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